1. Technical Field
The present invention relates to a fuel cell which causes fuel gas and gaseous oxidizer to react with each other therein so as to produce electricity. More particularly, it is concerned with a fuel cell which is constituted by stacking cell elements and separators one after the other, and a method of ameliorating temperature distribution of the fuel cell, each cell element being constituted by sandwiching an electrolyte such as fused carbonate by two electrode plates, and the fuel gas and the oxidizer being supplied through the separators.
2. Background Art
The principle of the fuel cell is as follows: hydrogen of the fuel gas and oxygen of the oxidizer are chemically reacted with each other with use of electrolyte, thereby producing electricity and water. This is the reversal of the electrodialysis of water. Major components of the fuel cell are cell elements, each of which elements includes an electrolyte plate, a porous anode plate and a porous cathode plate, with the electrolyte plate being sandwiched by the anode and the cathode plates. Electricity is generated by supplying the fuel gas to the anode side while supplying the oxidizer to the cathode side.
Herebefore phosphoric acid or fused carbonate was employed as the electrolyte of the fuel cell.
Reactions at the anode and the cathode plates, when the fused carbonate is utilized as the electrolyte, are as follows:
Cathode: 1/2O.sub.2 +CO.sub.2 +2e.fwdarw.CO.sub.3.sup.2- PA1 Anode: H.sub.2 +CO.sub.3.sup.2- .fwdarw.H.sub.2 O+CO.sub.2 +2e.sup.-
In the conventional fuel cell, the cell elements and the separtor plates are piled up alternately, making plural stages, and the fuel gas and the gaseous oxidizer are supplied to each cell element in a manner such that those gases flow along the upper and lower faces of the separator plate from one side of the separator plate to the other side thereof.
Meanwhile, since heat is produced upon generation of electricity in the fuel cell, certain measure has to be taken for elimination of such heat. Heat elimination, or cooling can be carried out by certain cooling means, or by continuous supply of fuel gas and oxidizer gas so that the previously supplied fuel gas and oxidizer and the fuel cell system may be cooled by the following gases. Gases introduced in a passage formed within the separator plate cool the cell element by receiving heat from the cell element as well as the separator plate until they reach the exit of the passage. In such a cooling, however, temperature distribution along the cell element face is not gentle, creating a considerable temperature difference of as large as three hundred degrees C. between the highest and the lowest temperature points thereof.
Such a large undulation in temperature profile along the cell element surface results in nonuniform current density, which in turn leads to deterioration of power generation efficiency of the fuel cell. Also, a sharp inclination in temperature distribution reduces longevity of the cell element and the separator.